Interactions among proteins are essential for the controlled function of all living cells, and inappropriate or adventitous protein-protein interactions are the hallmarks of virtually all diseases. Accordingly, biological probes directed at either the proteins themselves, or alternatively at their nucleic acid precursers, are essential for diagnosis of disease and general human health.
Existing biological probes are either nucleic acid-based or amino acid-based. Unfortunately, these prior art biological probes suffer from distinct and somewhat complementary disadvantages. Nucleic-acid based systems include oligonucleotides targeted for specific RNA or DNA sequences, which have the advantages of straightforward synthesis and simple rules for molecular complementarity. However, at present they can only be targeted easily to nucleic acids. Amino acid-based biological probes include antibodies, which can recognize a much broader range of molecules than nucleic acid-based probes. However, they are expensive and time-consuming to produce, requiring purification of the target and maintenance of animals. Moreover, functional antibodies cannot be expressed in intracellular compartments, and their use as biological probes often suffers from varying degrees of antigen expression, non-specific binding and adverse immunogenic reactions.
Accordingly, there is a significant need in the art for a biological probe with broader applications than oligonucleotides and antibodies. Such a probe should combine the advantages of nucleic acid-based probes--quick synthesis, intracellular expression and easy labeling in vitro--with the specificity of antibodies for peptide sequences. Ideally, these probes should be sensitive, stable and recognize a wide range of biological molecules having different biological functions.